The quality of a thermal processing brought about with the aid of an electron beam—for example, a weld—depends to a great extent on how accurately the working spot of the electron beam strikes the desired processing contour—in the case of the welding of two structural components, the groove path between the structural components to be welded—in the course of its relative motion in relation to the workpiece. In known material-processing methods of the type specified in the introduction, inaccuracies in this respect occur for differing reasons. A first reason consists in geometrical deviations between the actual processing contour and the expected processing contour stored in the control device, which in the following is also called the ‘ideal’ processing contour.
The geometrical deviations, in turn, may be both the cause of an inaccurate clamping of the workpiece and also the consequence of tolerance deviations to which the workpiece is subject in the course of manufacture. The consequence of these geometrical deviations is that although the working spot of the electron beam follows the ideal processing contour correctly, it does not strike the real processing contour or does not strike it everywhere. A second cause of deviations between the working spot of the electron beam and the actual processing contour may consist in the fact that a residual magnetisation is present in the workpiece, under the influence of which the electron beam is deflected. This has the consequence that the working spot of the electron beam does not strike the actual processing contour, even when the latter follows the stored ideal processing contour. These magnetically conditioned deviations therefore result in a behaviour that—judging from the outcome at any rate—is tantamount to a geometrical deviation of the actual processing contour from the ideal processing contour. A further cause of the working spot not striking the actual processing contour, or not striking it everywhere, may consist in errors in the programming of the motion.
In order to ensure that the working spot of the electron beam impinges everywhere on the actual processing contour, said working spot would have to be controlled in accordance with control variables that corresponds to a processing contour possibly deviating both from the ideal processing contour and from the actual processing contour, which here is called the ‘effective’ processing contour. If a magnetic deflection of the electron beam is eliminated, the effective processing contour corresponds to the actual processing contour.
The present invention is directed to resolving these and other matters.